You can draw a horizonatl rule by using four or more dashes.  The more dashes, the thicker the line:

|!c '''Markup Text'''|!c '''Displayed as:'''|
|!-above----below-!|!c above----!c below|
|!-above------below-!|!c above------!c below|
|!-above--------below-!|!c above--------!c below|
